Question: On the first 6 tests of his chemistry class, Kevin got an average score of 83. What does he need on the next test to have an overall average of 85?
Explanation: Let his score on the next test be $x$ The sum of all of his scores is then $6 \cdot 83 + x$ The same sum must also be equal to $7 \cdot 85$ Solve: $x = 7 \cdot 85 - 6 \cdot 83 = 97$.